eDRX (extended Discontinuous Reception)
Updated
eDRX lengthens the interval between the moments when a device listens for incoming messages from the network, from about a second to minutes or more. It was introduced by 3GPP in Release 13 for LTE-M and NB-IoT.
In practice
eDRX saves battery while keeping the device reachable within a known delay, a middle ground between always listening and PSM.